PURPOSE: To obtain a polymer excellent in heat resistance, soluble to organic solvents and controllable in depolarization degree and electrochemical oxidation- reduction potential, useful for films, etc., by reaction of a specific isoquinoline dihalide with a zero-valent nickel compound.

CONSTITUTION: An isoquinoline dihalide of formula I (X is a halogen) formed by halogen substitution of any two H atoms in quinoline is reacted with a zero-valent nickel compound, or preferably, the dihalide compound is electrolytically reduced in the presence of the nickel compound to obtain the objective polymer of formula II having a polymerization degree (n) of ≥5 made up of recurring constitutive unit i.e. a divalent group derived from the isoquinoline as a condensed heterocyclic compound by eliminating any two H atoms from the isoquinoline.